1. Technical Field
The present invention relates to a reference position detection device for a rotary mechanism that detects a rotational reference position within one revolution of a rotary member. A reference position detection device for a rotary mechanism of the invention can be used in a platen gap adjustment mechanism to adjust the gap between the printhead and platen in a printer.
2. Related Art
Printers such as inkjet printers commonly have a platen gap adjustment mechanism to adjust the gap between the nozzle face of the inkjet head and the platen, or the gap between the nozzle face and the printing surface of the print medium conveyed over the platen.
JP-A-2005-280206 and JP-A-2005-280209 teach printers having this type of platen gap adjustment mechanism. A carriage carrying the printhead is supported by two carriage guide rails in these printers. The two carriage guide rails are attached to an elevator frame, and the elevator frame is attached to move vertically on the side frame of the printer.
These printers transfer rotation of the elevator motor attached to the printer frame through a geared rotary mechanism to a carriage guide rail. Rotation transferred to the carriage guide rail is then transferred to a gear train of multiple spur gears to the other carriage guide rail. At the end of each carriage guide rail is a cam mechanism that changes rotation of the carriage guide rails to vertical movement of the carriage guide rails. When the carriage guide rails rotate synchronously, the cam mechanism causes the carriage guide rails to move vertically synchronously, and the gap between the recording head on the carriage and the platen on the stationary side changes.
Adjusting the platen gap is controlled based on the rotational position of the rotary mechanism that is part of the platen gap adjustment mechanism. During the initialization operation, the reference position (home position) is detected within one revolution of the rotary member of the rotary mechanism, the amount and direction of rotation of the rotary member are controlled based on the reference position, and the platen gap is adjusted.
JP-A-H08-189596 discloses a reference position detection device for a rotary mechanism. This device has a detection flag that protrudes to the outside from the outside of a rotary member, and a transmissive photosensor disposed to a fixed position on the outside of the rotary member. The transmissive photosensor detects the edge of the detection flag rotating in unison with the rotary member, and the rotational position of the rotary member when the edge is detected is set as the reference position of the rotary member.
In the reference position detection device of the rotary mechanism according to the related art the detection flag turns one revolution with the rotary member. Space for the rotating detection flag to move must therefore be provided around the entire outside circumference of the rotary member. Parts disposed outside the rotary member must therefore be located outside the space through which the detection flag moves. The required outside diameter of the reference position detection device therefore increases, and the device cannot be made small and compact.
The platen gap adjustment mechanism of a printer is generally disposed on the side of the width of the paper conveyance path. Components of a transfer mechanism that transfers rotation to the paper conveyance roller, for example, are disposed beside the paper conveyance path. Providing sufficient space sufficient to assemble a platen gap adjustment mechanism may therefore not be possible. A small, compactly configured reference position detection device for a rotary mechanism assembled in a platen gap adjustment mechanism would therefore be extremely useful.